1. Field of the Invention
This invention relates to an aluminum alloy for galvanic (sacrificial) anode which is used for cathodic protection of facilities in sea water, vessels and machineries using sea water, and the like.
2. Description of the Prior Art
Normally, aluminum is stable in a neutral solution by virtue of an oxide film, and has a potential less noble than steel. Accordingly, aluminum has been added with various effective elements so that it has a sufficiently base potential and generates a protective electric current as a galvanic anode for use in cathodic protection.
Inventors of the present invention have carried out a series of studies and developments based on alloys which comprise incorporating zinc and indium in aluminum. Consequently, our inventors have previously developed alloys for galvanic anode (Japanese Patent Publication No. 2139/1982) containing zinc of 1.0 to 10%, magnesium of 0.1 to 6%, indium of 0.01 to 0.04%, tin of 0.005 to 0.15% and silicon of 0.09 to 1.0%, the balance being aluminum, and alloys for galvanic anode (Japanese Patent Publication No. 14291/1967) containing zinc of 1.0 to 10%, indium of 0.01 to 0.05% and magnesium of 0.05 to 6%, the balance being aluminum, and both have been patented. The former alloys were effective for increasing the uniformity of anodic dissolution, which had been a somewhat hard point to settle, and which continuing a large current capacity stably for a long period by adding a proper amount of silicon. The latter alloys aimed at uniform dispersion of indium by adding a small amount of magnesium to thereby improve anode performance. Referring to the anode performance of these alloys, the anode potential was in the range of -1080 to -1100 mV (based on saturated calomel electrode) and the current capacity (effective ampere hour) was about 2400 to 2600 Ahr/Kg.
However, these alloys were not always satisfactory in the current capacity when applied, as anodes, for use to large-sized steel structures as such steel structures come into wide use, and so development of alloy anodes, which are capable of yielding a much more current capacity, has been demanded eagerly.